On newer boats, Catalina added a "u-shaped" bracket attached to the inside of the hatch (many hatches on the boat) with a short vinyl-coated lanyard and hook attached to it. When open, the hook on the lanyard can be clipped to a lifeline or other suitable attach point, effectively holding the hatch in the open position.
As a retrofit, I suppose that attaching a small wooden flat block to the inside of your hatch, using the dreaded 5200 or other strong adhesive, would give you something to attach the U-shaped fitting to the inside of the hatch without having to worry about blowing a screw through the material, or having the screws not take a bite in the fiberglass.
Wouldn't have to be wire lanyards either, could be light rope.
Good Luck!
Tim Brogan
April IV C350 #68
Seattle